Hottest temps ever at LHC, and more hints about early Universe

An odd asymmetry that may explain why there's more matter than antimatter.

Washington, DC—This week is the Quark Matter 2012 (QM2012) conference—the preeminent meeting for those studying high-energy collisions between heavy ions. I attended a number of talks on Monday, August 13, during which researchers announced the major new results from the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory and the Large Hadron Collider (LHC) at CERN. The conference offered fresh insights on the transition between ordinary matter and the soup of quarks that existed in the early Universe—including a tantalizing hint that might tell us about why the modern cosmos has more matter than antimatter.

We recently ran a detailed review of heavy-ion physics; here's an executive summary. Heavy nuclei (lead at LHC, gold, copper, and uranium at RHIC) are completely stripped of electrons, leaving massive, positively charged ions. These are accelerated to well over 99 percent of the speed of light and smashed into each other. If the energy is sufficiently high, the protons and neutrons in the nuclei "melt" into their constituent quarks and gluons. The result is a substance known as the quark-gluon plasma (QGP), which theory predicts existed during the first 10 microseconds after the Big Bang.

While the hunt for the Higgs boson has dominated press coverage of the LHC, the collider also performs heavy ion experiments using lead (Pb+Pb). In addition to the ATLAS and CMS detectors, which are used both for proton-proton and heavy ion collisions, LHC has a dedicated heavy ion detector named ALICE (A Large Ion Collider Experiment, pronounced "ahLEES"). The two active detectors at RHIC are PHENIX (Pioneering High-Energy Nuclear Interacting Experiment) and STAR (Solenoidal Tracker at RHIC). These study the products of collisions between gold ions (Au+Au); in the most recent experiments, researchers have added gold and copper asymmetric collisions (Au+Cu) and uranium (U+U). The two major colliders are complimentary in many aspects: the LHC has a larger temperature range and can reach lower density, while RHIC is able to explore much higher baryon densities.

To form a more perfect fluid

The detectors at RHIC and LHC measure the particles produced within the QGP, and those formed in the first stages of the collision and pass through the plasma. Many of these particles are hadrons (collections of quarks), but many photons, electrons, and muons are made, some from the decay of exotic species containing strange and charm quarks.

The distribution of the collision products reveals a lot about the interaction between the ions when they collide—including their positions within the region of overlap. Just as Fourier analysis reveals the harmonics contained in a musical note, researchers use it to determine the shape of particles coming out of the QGP. This result in turn reveals a lot about the plasma itself: if it had high viscosity, then the deformations would be damped out, just as a stiff mixture resists carrying waves over long distances. However, because the deformations are carried through, that means the QGP has low viscosity.

The "melting" analogy I used above appears to be appropriate for talking about the transition from stable nuclei to the QGP. While we are often used to thinking of plasmas as gaseous (like they are in stars), the QGP is actually a liquid that flows with nearly zero viscosity. Viscosity is the resistance to flow: water has relatively low viscosity, but the QGP has much less. Theoretical models predict that viscosity can never be zero due to quantum fluctuations, but as Jurgen Schukraft of CERN described it, the QGP's viscosity is very close to the predicted minimum.

Several speakers emphasized how new that result is: three years ago, nobody suspected the deformations could be studied in that much detail, but today they are some of the most powerful data coming from detectors.

The phase diagram of QCD matter, showing the possible states quarks have. Ordinary matter lies at the bottom left corner, where temperature and density of matter are both relatively low. RHIC and LHC explore much higher energies; currently RHIC researchers are hunting for the possible existence of a critical point, where stable hadrons may mingle with the quark-gluon plasma.

Much of the recent work at RHIC and LHC is an attempt to map the phase diagram of the dense hot matter formed in these collisions (called "QCD matter" in reference to quantum chromodynamics, which describes its behavior). The people running the accelerators are trying to map the transitions between the QGP, ordinary matter, and other phases. Ordinary phases of matter include solid, liquid, and gas; physicists add many more, such as various magnetic and superconducting phases.

Water provides an analogous situation to QCD matter: at low temperatures and moderate pressures, it exists as ice, while at higher temperatures it may melt into liquid or boil. However, at higher temperatures and pressure, water reaches a critical point: a place where it is a fluid, but there is no longer a distinction between the liquid and vapor state.

For QCD matter, the relevant quantities are temperature (a proxy for energy) and density of matter. At low temperatures and high density, the result is stable hadrons. At higher temperatures, hadrons melt into the QGP. (At relatively low temperature but extremely high densities, matter forms yet another phase we don't understand very well: the substance that comprises neutron stars.)

Experiments at RHIC have begun probing the phase transition between stable hadrons and the QGP—and looking for a possible critical point. While this critical point hasn't been found yet, there are good theoretical and experimental reasons to think it exists. At QM2012, Steve Vigdor (associate laboratory director for nuclear and particle physics at Brookhaven) pointed out that STAR has seen signs of a transition between QGP and stable hadrons, where the strange quark production seen at higher energies dropped precipitously.

Golden hints about the early Universe

Earlier low-energy RHIC experiments using gold (Au+Au) found electric polarization—a small separation of positive and negative charges—in the overlap region where the ions collided. This effect was potentially worrying, since quantum chromodynamics requires chiral (or mirror) symmetry: there should be no inherent left- or right-handedness resulting from strong force interactions. However, QCD does allow violations of this symmetry at higher temperatures, such as those in the QGP, as long as they average out over all collisions. These violations may have played a role in the early Universe, when more matter was produced than antimatter, according to BNL's Vigdor.

Au+Au collisions result in strong magnetic fields, which complicate analysis. The uranium-uranium collisions have effectively ruled out the possibility that the charge separation is due to the specific shape of the overlap region in the Au+Au interaction. This test was possible because uranium nuclei are highly non-spherical, having nearly the shape of an American football. RHIC researchers collided uranium ions both along their long sides and their narrow ends. The end-to-end collisions resulted in very high energy density, said Stony Brook physicist Barbara Jacak, while the side-to-side collisions produced charge separation without magnetic field effects.

Similarly, the asymmetric gold-copper collisions may hold clues to whether the symmetry violation is a fundamental result, or an artifact of the experimental setup. However, it's too early to draw strong conclusions (Jacak told me the Au+Cu collision results are only a few weeks old), so further analysis will need to happen before we can definitively say if the charge separation has anything important to say about QCD or the QGP.

More exotic quark matter

With much higher energies available at LHC, researchers are using it to examine a high-temperature region of the QGP: the strongly correlated QGP (sQGP). ALICE found that particles passing through the sQGP experienced a great deal of energy loss, suggesting the interactions within it are different from those present at lower energies. The sQGP is still poorly understood from a theoretical point of view, according to CERN theorist Urs Achim Wiedemann.

Analogous systems exist in condensed matter physics (which are very low temperature), but the particle-like excitations that drive so much of the interesting behavior in materials don't seem to exist in the QGP. However, both the theoretical and experimental studies of the sQGP are in very early stages.

To give a sense of how preliminary they are: CERN announced yesterday that the LHC has achieved the highest human-made temperatures yet, but hasn't been able to determine exactly what that temperature is. It's about 38 percent larger than the previous record from RHIC, which was about 4 trillion degrees Celsius. Such high energies should help make clear the structure of the sQGP.

Promoted Comments

Did anyone else find it fascinating that the researchers were able to selectively orient the Uranium atoms?

I did as well.. Although, I think you mean Uranium ions, right?

The uranium ions are rotating randomly the accelerator has no influence on that, all we can do is figuring out from the distribution of produced particles which way they might have been oriented, both experiments have specialized detectors that help with that.

However, QCD does allow violations of this symmetry at higher temperatures, such as those in the QGP, as long as they average out over all collisions. These violations may have played a role in the early Universe, when more matter was produced than antimatter, according to BNL's Vigdor.

That's pretty neat.

I've seen an explanation of the reason for there being more matter than antimatter as being something along the lines of a slight difference in mass between the two (from Lawrence Krauss's book, but there's probably a paper on it somewhere). I haven't studied physics, so I'm not certain what the implication of "These violations may have played a role" really means. The article seems to only discuss the asymmetry. Has anyone got an (hopefully lucid) answer?

Why does the RHIC have two separate, disjoint operating regions instead of a single range encompassing both areas? Is this a design limitation; or do the two ovals just indicate the subset of the potential performance envelope that has been extensively studied?

Why does the RHIC have two separate, disjoint operating regions instead of a single range encompassing both areas? Is this a design limitation; or do the two ovals just indicate the subset of the potential performance envelope that has been extensively studied?

RHIC use of different elements for their ions may have some bearing on this?

Another question; what exactly does density refer to in terms of the RHIC/LHC research? Do higher densities mean the initial lumps of QGP formed by the collisions of two ions are more compact, a higher density of ions in the beams used to create them (and presumably a greater number of QGPs produced over a given time period), or something else?

This is really interesting. Thanks! As a minor point, my understanding is that viscosity is resistance to shear in fluids, not flow.

Shear or tensile stress, although shear stress is typically the important part to do with flow (but tensile can be a factor) since flow tends to create shearing in the fluid, and thus viscosity is in effect resistance to flow.

This is really interesting. Thanks! As a minor point, my understanding is that viscosity is resistance to shear in fluids, not flow.

Shear or tensile stress, although shear stress is typically the important part to do with flow (but tensile can be a factor) since flow tends to create shearing in the fluid, and thus viscosity is in effect resistance to flow.

Why does the RHIC have two separate, disjoint operating regions instead of a single range encompassing both areas? Is this a design limitation; or do the two ovals just indicate the subset of the potential performance envelope that has been extensively studied?

If i am reading you correctly, the smaller oval gets the matter up to speed, while the larger oval is where the collisions take place.

I remember the first time I got in contact with high temperatures theories, it was when I was ~14 and just got told about absolute minimum temp (0K − 273.15C....) and of course needed to ask since there's a minimum is there a max? My science teacher didn't know and obviously had not prepared for that question, it was interesting to see a teacher not have the slightest idea of what/how explain max temperatures...

4 trillion degrees C is kind of high, especially when you complain about 30 C being to hot...

I remember the first time I got in contact with high temperatures theories, it was when I was ~14 and just got told about absolute minimum temp (0K − 273.15C....) and of course needed to ask since there's a minimum is there a max? My science teacher didn't know and obviously had not prepared for that question, it was interesting to see a teacher not have the slightest idea of what/how explain max temperatures...

4 trillion degrees C is kind of high, especially when you complain about 30 C being to hot...

I wondered the same thing when I learned about absolute 0 in chem class.

That's what I don't get about CERN. The acronym has not been accurate for 60 years but they still use it - but another batch of scientists won't let pluto remain a planet.

I might start believing in god if science is going to be this crazy.

CERN = Centre Europeén pour la Recherche Nucléaire = European Center for Nuclear Research. You mean because they now investigate the components of the Nucleus and its origins, using nucleii, they no longer merit the name?

So these bubbles of broken symmetry, in the cosmological hypothesis abstracting to matter-antimatter, are larger than primordial fluctuations which we see as galaxy cluster filaments after inflation, and encompass something much larger than the observable universe?

Still, any other symmetry breaking before or during that process could affect the probability that a volume ends up with matter instead of antimatter. Sort of an anthropic spice to the dish.

Why does the RHIC have two separate, disjoint operating regions instead of a single range encompassing both areas? Is this a design limitation; or do the two ovals just indicate the subset of the potential performance envelope that has been extensively studied?

TylerX Durden was here already. AFAIK RHIC can collide light ions, which would make it parallel LHC @ high energy (temperature) and low density in the collision region*, or it can collide heavy ions like uranium @ low energy (temperature) and high density.

The distinct regions shown may be more for illustration than actual operation. But sure, they would want to complement some of LHC work as well as follow the phase change region, so it can also be an illustration of most use.

* I believe this answers your next Q as well, but bear in mind I am no particle physicist. Needs checking.

Tyler X. Durden wrote:

Quote:

While we are often used to thinking of plasmas as gaseous (like they are in stars), the QGP is actually a liquid that flows with nearly zero viscosity.

I find this a very puzzling statement as plasma is considered neither a gas nor a liquid by definition?

It seems you are dancing back and forth between analogy and not-analogy without clear indication of the switches.

People use approximations (models), sometimes only partial (analogies - sort of), when it suits. No one will make much of it, as long as it is accepted or understandable use.

To make matters worse, different areas use different models. In astronomy _all_ plasma (IIRC) is "gas" because it is either very dilute or in hydrostatic equilibrium (stars). Except when you need to take into account its plasma behavior, natch.

You should hear the pseudoscience religious of the churches of "Plasma Cosmology" and "Electric Universe" when they 'feel oppressed by the majority, who obviously conspire'. (O.o)

Dravond wrote:

I remember the first time I got in contact with high temperatures theories, it was when I was ~14 and just got told about absolute minimum temp (0K − 273.15C....) and of course needed to ask since there's a minimum is there a max?

It isn't all that well defined, with equilibrium temperatures missing, at least in our recreation attempts of the early universe.

Or more precisely, to have a temperature that reminds of thermodynamics (TD) you need to have some sort of energy distribution that the particles sits at. That is the whole point of TDs distinction between "intensive" (averaged, as temperature) and "extensive" (additive, as energy) parameters.

Most often you convert energy to an equivalent temperature and hold your tongue. "Shut up and calculate!"

I remember the first time I got in contact with high temperatures theories, it was when I was ~14 and just got told about absolute minimum temp (0K − 273.15C....) and of course needed to ask since there's a minimum is there a max? My science teacher didn't know and obviously had not prepared for that question, it was interesting to see a teacher not have the slightest idea of what/how explain max temperatures...

4 trillion degrees C is kind of high, especially when you complain about 30 C being to hot...

I imagine the hottest "Temperature" would be the total measurment of all the matter in the universe being converted to energy, plus the energy. So essentially, impossible to reach in practical terms unless you start another big bang. As for a number, I have no friggin clue how incalculably huge it may be.

While we are often used to thinking of plasmas as gaseous (like they are in stars), the QGP is actually a liquid that flows with nearly zero viscosity.

I find this a very puzzling statement as plasma is considered neither a gas nor a liquid by definition?

It seems you are dancing back and forth between analogy and not-analogy without clear indication of the switches.

People use approximations (models), sometimes only partial (analogies - sort of), when it suits. No one will make much of it, as long as it is accepted or understandable use.

To make matters worse, different areas use different models. In astronomy _all_ plasma (IIRC) is "gas" because it is either very dilute or in hydrostatic equilibrium (stars). Except when you need to take into account its plasma behavior, natch.

Just use the term “fluid” people, damn it. Plasmas are fluids, as gases and liquids. And they all have viscosity to some degree, though the mechanics of it differs.

It would be so much clearer to say that plasma is different than a gas or a liquid and while it shares a number of similarities with gases, ones that astrophysics typically care about, it also has some characteristics closer to liquids. For example gases are essentially electrically non-conductive, while plasmas are quite conductive as are a number of liquids (if they have ions in solution, or are metals), or pertinent to this situation how they behave as they flows.

Is that what they were getting at?

Quote:

You should hear the pseudoscience religious of the churches of "Plasma Cosmology" and "Electric Universe" when they 'feel oppressed by the majority, who obviously conspire'. (O.o)

I tried to read some Electric Universe once, because I was curious…and just taking some Authority Figure’s word that someone is batsht insane doesn’t sit well with me. I got about 3/4 of the way through a couple different…tracts before deciding maybe masochism wasn’t my bag so I stopped reading it. I’m such a wimp in the face of so much Crazy.

This machine will not "discover" much mainly for a seriously flawed assumption that the "state of matter" is the same at the Big Bang as it is now. This is so far from the truth, it is laughable!. Even at the centre-of-the-sun, the "state of matter" is complexly different from the state of matter on earth. It goes for the Higgs field not being anything constant either based on the interactions of nearby particles (what type, at what pressure, what temperature, at what state). Also, some so-called multi-dimensional subparticles to zips in and out of our reality. There are many many variables not accounted for. Most being ignored as in past what scientists have done. So I cannot account for any result/discoveries they claim to have. Our particle physics is very primitive because scientists are "forced" the dogma of "known science" much like a religious belief. Many have said Science has been used as a new religion and it is effectly true for people pushing their particular agenda their way for their own reasons. It is why secrecy exists still and more so.

How do the scientists know that at max Planck temp that matter behave the same as lower temps ?. It could turn into a new type of gaseous matter we have never seen before and has properties that are too weird to be constant. ie can see, cannot get a consistent measurement, or consistent mass estimation ?.

Why does the RHIC have two separate, disjoint operating regions instead of a single range encompassing both areas? Is this a design limitation; or do the two ovals just indicate the subset of the potential performance envelope that has been extensively studied?

The envelope for the RHIC that follows the LHC's envelope is what can be achieved just using the RHIC as a brute force accelerator. For the RHIC, this envelope has been fully explored, the RHIC simply doesn't have the power output to go head to head with the LHC on luminosity. The LHC on the other hand doesn't have the ability to spin polarize particles, and can only run heavy particles for a few weeks a year.

Just use the term “fluid” people, damn it. Plasmas are fluids, as gases and liquids. And they all have viscosity to some degree, though the mechanics of it differs.

Oh, I agree. And physics should change the polarity of EM charges so that everyday electric currents (charge flows) are traveling in the same direction as the particle fluid. And mathematics should change coordinate systems so positive turns are clockwise! [/pouts]

Tyler X. Durden wrote:

It would be so much clearer to say that plasma is different than a gas or a liquid and while it shares a number of similarities with gases, ones that astrophysics typically care about, it also has some characteristics closer to liquids. For example gases are essentially electrically non-conductive, while plasmas are quite conductive as are a number of liquids (if they have ions in solution, or are metals), or pertinent to this situation how they behave as they flows.

Is that what they were getting at?

If I understand your question correct, yes. Seems for them a "gas" is when particles behaves as a gas, even if they happen to be ionized.

Of course there is a fuzzy limit between non-ionized gases and ionized plasmas as you increase the degree of ionization. And the same goes for the limit between dense gas fluid flows and near vacuum molecular flows (when viscosity drops to essentially zero and gas flows can superposition freely, traveling in different directions).

So there is no definition saving us from ambiguity, as it were.

Tyler X. Durden wrote:

some Authority Figure’s word

Oh wow, I haven't even tried reading that stuff.

That was both funny and convoluted. As a skeptical outsider in a science area, I do tend to take the consensus position until I feel well informed on the context. It is useful.

But of course you can discover that the area isn't well settled, and the consensus can be dated or biased. Cosmology, or at least popular cosmology, is like that when you get back to the inflation era before the reheating we study above. The notion that an isolated big bang singularity could uniquely constrain a Theory Of Everything is still biasing the descriptions ("the Big Bang"), even when stuff like these bubbles of charge separation rejects the notion (or at least as deciding the full parameter set for our universe).

The funny part is the term "Authority Figure", because it seems to me there are people that have an "authority complex", as some variant on inferiority complex perhaps. Authorities can be awesomely wrong, as well as awesomely prescient. (Say, Einstein on quantum theory and general relativity for the latter, and - Einstein on quantum theory and general relativity (!) on the former: QM hidden variables, GR effective theory part of a fundamental theory.)

I don't think people that are interested in science has much patience with AFs outside of education. Or at least, I hope so. As opposed to accepting the consensus, it is a much riskier way to assess the state of the art in an area.

"These violations may have played a role in the early Universe, when more matter was produced than antimatter, according to BNL's Vigdor."

I am not a scientist.

But i do love they way us puny humans say that thing 'A' violates such and such a Law, we made the law nature does not obey us, we just have our Law's wrong or at very least not quite right.

No, that is a misunderstanding. It is a technical notion.

It can span everything from actually violating "a law" with another, such as when uncertainty principles violate thermodynamical laws within tight limits, to when a symmetry is "broken", the system can choose one minima which appears asymmetric.

This latter is what happens with these charge bubbles, the theory is symmetric, the outcome is not.

The former can be what you describe, but it can also be because there is a fundamental reason for such violations. QM vs TD is like that, both can be formulated on the microstate level and, lo and behold, they mesh together "violatingly".

While I am concerned with the implied (brutal) anthropomorphism I am not at all concerned with ludicrous theological implications. Nature do obey us, there was no QCP plasma in these accelerators before we put it there, and on top of that we observably have the ability to change natural constraints ("laws"). That is what we did with artificial selection in biology, for example, which humans already did ~ 30 - 35 000 years ago. (Finds of dog analogs before the last ice age; I am uncertain of the date.)

In principle we could make new universes with new laws as much as physics admit that universes spawns new universes. For reasons of thermodynamics we can't initiate a bubble universe, I think, because they are zero energy so no third party can make them. But we could feasibly affect the probability that a bubble transition happens. (Aka the Ultimate Doomsday Weapon. Oops.)

This machine will not "discover" much mainly for a seriously flawed assumption that the "state of matter" is the same at the Big Bang as it is now. This is so far from the truth, it is laughable!. Even at the centre-of-the-sun, the "state of matter" is complexly different from the state of matter on earth.

You are describing what this article is talking about and has already happened as part of this work. They are looking further back and indeed finding new information about likely state of matter along a point on the timeline. Further, yes some current assumptions will be shown wrong but the more pieces that fall into place (an explanation of the [apparent] matter-to-antimatter imbalance) the more solid the confidence we can put in the overall. Really, even if nearly all assumptions we make now bear out as incorrect those assumptions are very useful as a jumping off point to work from. Another name for an assumption is a hypothesis to test.

Quote:

How do the scientists know that at max Planck temp that matter behave the same as lower temps ?. It could turn into a new type of gaseous matter we have never seen before and has properties that are too weird to be constant. ie can see, cannot get a consistent measurement, or consistent mass estimation ?.

? This work does NOT represent investigation into conditions at Planck temp, but later than that in the early universe history. Planck temp is generally pegged at 10^-43 sec and earlier. This work is concerned with the single digit millisecond range, which is an enormously different ball of wax.

Incidentally Planck temp is only referred to as the max temp because our [currently widely agreed upon] mathematical models for physics break at that point. That means it is a good guess that something happens at, or potentially below, that temperature that requires a different physics model. We assume the 4 fundamental forces don’t exist, at least not separately, at and above that point.

Just use the term “fluid” people, damn it. Plasmas are fluids, as gases and liquids. And they all have viscosity to some degree, though the mechanics of it differs.

Oh, I agree. And physics should change the polarity of EM charges so that everyday electric currents (charge flows) are traveling in the same direction as the particle fluid. And mathematics should change coordinate systems so positive turns are clockwise! [/pouts]

Of course there is a fuzzy limit between non-ionized gases and ionized plasmas as you increase the degree of ionization. And the same goes for the limit between dense gas fluid flows and near vacuum molecular flows (when viscosity drops to essentially zero and gas flows can superposition freely, traveling in different directions).

So there is no definition saving us from ambiguity, as it were.

The plasma-gas boundry for categorization is somewhat fuzzy, I understand there is somewhat “I know it when I see it” standard for these two, but I’m talking about a different matter here.

Quote:

Tyler X. Durden wrote:

some Authority Figure’s word

Oh wow, I haven't even tried reading that stuff.

That was both funny and convoluted. As a skeptical outsider in a science area, I do tend to take the consensus position until I feel well informed on the context. It is useful.

…

The funny part is the term "Authority Figure", because it seems to me there are people that have an "authority complex", as some variant on inferiority complex perhaps.

That was largely tongue-in-cheek. Darn text medium.

I looked it up because, well I hadn’t seen much from the person themselves. What small comment they made sounded funky, oh boy I had no idea just how far out there they were, but I like to double-check on my view of someone’s batshititude, and be able to give something resembling a reasoned explanation of it, before asserting it out loud.

EDIT: I did find it informative to read what I did because it became readily apparent what the fundamental misunderstandings and fallacies it is based upon. Also I expect I’ll be much more prepared to quickly identify the coded messages (they seem to use certain key phrases repeatedly, to bundle up all these fallacies inside) so I can save myself time identifying that particular brand of batshitite when I run into them, again.

Why does the RHIC have two separate, disjoint operating regions instead of a single range encompassing both areas? Is this a design limitation; or do the two ovals just indicate the subset of the potential performance envelope that has been extensively studied?

RHIC use of different elements for their ions may have some bearing on this?

RHIC has two independent accelerator rings that are combined into one tube at 6 interaction points, two of these have experiments, the others accelerator and monitoring equipment. Having two independent rings makes RHIC so versatile. There are some nice pages under http://www.bnl.gov/rhic

Did anyone else find it fascinating that the researchers were able to selectively orient the Uranium atoms?

I did as well.. Although, I think you mean Uranium ions, right?

The uranium ions are rotating randomly the accelerator has no influence on that, all we can do is figuring out from the distribution of produced particles which way they might have been oriented, both experiments have specialized detectors that help with that.